Project Summary/Abstract HIV incidence rates are disproportionately high among young adult (ages 18-30) men who have sex with men (MSM), in part due to overlapping risk-factors, such as high rates of alcohol use. Pre-exposure prophylaxis (PrEP) is an efficacious HIV prevention drug, but has little utility without strong adherence. The potential for risk compensation ? an increase in sexual risk-taking (e.g., more condomless sex) as PrEP users believe their risk for HIV is reduced ? is another considerable concern with PrEP, because PrEP does not protect against other sexually transmitted infections (STIs). Substantial evidence indicates that alcohol facilities the spread of HIV by increasing sexual risk-taking and reducing medication adherence, exacerbating both critical concerns with PrEP ? increased sexual risk-taking and reduced PrEP adherence. However, alcohol has received little attention in the PrEP and risk compensation literature, with only two studies reporting on alcohol use. Further, research on PrEP and risk compensation is replete with methodological limitations, including an exclu- sive reliance on retrospective self-reports and largely consists of cross-sectional studies. Research examining PrEP and risk compensation is inconclusive, in part due to these limitations. There is an urgent need to address this as a quarter of physicians report unwillingness to prescribe PrEP due to risk compensation concerns. Thus, the proposed study will address these gaps and limitations by determining the effects of PrEP and alcohol use on sexual risk-taking by using novel behavioral measures before and after PrEP uptake. The proposed project will use the Sexual Delay Discounting Task (SDDT) pre- and post-PrEP uptake to examine changes in HIV sexual risk-taking and determine associations with alcohol use, demand and reinforcement. The SDDT is a novel measure of sexual risk-taking that minimizes retrospective self-report, is reliable and valid, yet underutilized. The SDDT assesses impact of partner STI/HIV status and condom availability on likelihood of condom use, and has shown stronger relations to clinical outcomes, compared to self-report and other discount- ing measures. Despite this promising supporting evidence, the SDDT has not been used as an outcome measure in intervention studies. This study will establish validity of the SDDT as an outcome measure for future studies, providing a novel target for research testing interventions to reduce alcohol use and sexual risk-taking. The proposed F31 will enhance a NIAAA-funded randomized control trial (UH2/UH3AA026214, Leeman) testing a mobile intervention to reduce alcohol misuse and enhance PrEP adherence. Heavy drinking young adult MSM (N = 80) will receive open-label PrEP for 30 days, with a follow-up at 6-months. A no treatment control group (no PrEP; no intervention; N = 40) will be added for the F31 to complete study measures following the same timeline. This F31 will enable the applicant to work with a highly-skilled, experienced training team to develop proficiencies in: (1) randomized controlled trial and experimental methods; (2) application of behavioral economics; and (3) longitudinal data analysis to prepare for a career as independent investigator in alcohol/HIV research.